Referring to FIGS. 11 and 12, an example of a prior art needle roller thrust bearing 1 is shown. The bearing 1 includes a plurality of cylindrical rolling elements 2 arranged radially from a center of rotation. The rolling elements 2 are retained and guided by a bearing cage 3, which forms the primary structure of the bearing 1.
There are several types of construction currently used to produce metallic needle roller bearing cages 3. FIGS. 13 and 14 show a thrust bearing 1A with a cage 3A that is constructed of two halves 4. Each half 4 has rectangular window openings 5 which are slightly smaller in width than the diameter of the rolling elements 2. Each cage half 4 also has circumferential flanges 6 which are directed inwardly towards the opposite member. When joined together, these two cage halves 4 form a box which provides structural integrity for the assembly, along with guidance for the rolling elements 2 and their retention in both directions.
A prior art thrust bearing 1B with a cage 3B having another construction is shown in FIGS. 15 and 16. In this construction, the cage 3B is formed from a single piece of metal into a shape which, along with specially shaped openings, retains and guides the rolling elements 2. In cross-section, this type of cage 3B has a shape similar to that of the Greek letter sigma (Σ).
Another thrust bearing 1C having a cage 3C of yet another construction is shown in FIGS. 17 and 18. Here, the cage 3C has a material thickness close to the diameter of the rolling elements 2 and has rectangular openings 5 to accept the rolling elements 2. Retention is provided by staking 7 or otherwise forming the cage face near the openings 5 so that these are made smaller than the diameter of the rolling element 2.